Dynamic Of Multi-filament Interaction And Quantum Phase Control In Atomic And Molecular Systems

Due to the dynamic-balance between the Kerr self-focusing effect and the plasma defocusing effect, filament channels can be formed during the self-guided propagation of ultrashort intense laser pulses. Recently, plasma grating can be generated by two-noncollinear-filament interaction, which exhibits captivating properties for further research. With femtosecond laser filamentation as the research object, the first part of this thesis is mainly done as the following:First, supercontinuum conical emission (SC CE) accompanying the filamentation of powerful ultrashort laser pulse in BK7 glass and fused silica is studied, combining with a numerical simulation. The laser power density and the sample thickness can control the intensity of the SC CE. The angular distributions of the SC CE in the wavelength range less than 510 nm are measured, which can’t be explained by the Cerenkov emission theory but the unabridged X-Waves solution theory.Second, the influences of the plasma grating on the plasma fluorescence and the third harmonic (TH) generation of the probe filament are studied. The continuum radiations and the linear radiations of the plasmas fluorescence are used to investigate the dynamics of multifilament interaction. TH generation can be enhanced by more than three orders of magnitude and significantly broadened by the plasma grating. The intensity of TH generation depends on the time delay, the spatial period of plasma grating, the relative polarization between the probe beam and the plasma grating.Then, we study the supercontinuum generation, the energy exchange process and the spatiotemporal pulse-splitting by applying a plasma grating. The supercontinuum generation and the core energy of a probe pulse as functions of the time delay, the relative polarization referencing to the plasma grating are measured together with the far-field spatial profiles of the three pulses. An energy transfer ratio up to 42% of the probe pulse is detected between the probe pulse and the plasma grating, and the energy transfer ratio and directions depend on the time delay. The energy exchange process is interpreted by the time-domain model, and the delayed nonlinear refractive index coefficient is extracted. Via interacting with a plasma grating with a large crossing angle, spatiotemporal pulse-splitting of the filamentary probe pulse is detected with separated distances in 102 μm magnitude, and the separated distances depends on the crossing angle between the probe pulse and the plasma grating. Combining with theoretical calculation, a reasonable explanation for the spatiotemporal pulse-splitting is obtained.The interaction of light with matter can be described via the dipole-response function which is directly proportional to the system’s polarizability. Most recently, increasing attention was received by related studies of quantum dynamics in which the arrival order of the pump and probe pulses is inverted, i.e., in which one measures the absorption spectrum of the initial pulse triggering the dynamical evolution of the system. The pump pulse can be used to subsequently modify the system’s dipole response shown by the change of absorption line shape, known as the phase-control mechanism. Basing on this concept, we study the phase-modulation of optical dipole response in various systems as following:First, a general mechanism for the generation of frequency combs referenced to atomic resonances is put forward, which is based on the periodic phase control of a quantum system’s dipole response. We develop an analytic description of the comb’s spectral structure, depending on both its atomic and phase-control properties. We further suggest an experimental implementation of our scheme, i.e. generating a frequency comb in the soft x-ray spectral region, which can be realized with currently available techniques and radiation sources. The universality of this mechanism allows the generalization of frequency comb technology to arbitrary frequencies, including the hard x-ray regime, by using reference transitions in highly charged ions. Afterwards, the phase control concept is generalized to a more complex system IR144 in methanol. Numerical simulations support the interpretation of the experimental results. Thereby, the general phase control concept is transferred to transient-absorption measurements in the liquid phase and its universal applicability is demonstrated.Then, we study the evolution of a V-type three-level system, whose two resonances are coherently excited and coupled by two ultrashort laser pulses separated by a varying time delay. We relate the quantum dynamics of the excited wave-packet to the absorption spectrum of a transmitted probe pulse. In particular, by analyzing the quantum evolution of the system, we interpret how atomic phases are differently encoded in the time-delay-dependent spectral absorption lines when the pump pulse either precedes or follows the probe pulse. We experimentally apply this scheme to atomic Rb, whose spin-orbit split 5s2S1/2â†'5p 2P1/2 and 5s2S1/2â†'5p2 EP3/2 transitions are driven by the combined action of a pump pulse of variable intensity and a delayed probe pulse. The pump pulse is shaped by a pulse shaper, and the corresponding transient-absorption spectroscopy is studied. Two pump pulses are also applied to measure the absorption spectra of the probe pulse. The pump pulses favor either one of the two transitions and eventually even decouple the two excited states, which depends on the pump-pulse-intensity.